Catalyst for the production of allyl acetate

ABSTRACT

A process and catalyst for the acetoxylation of propylene, said catalyst consisting essentially of palladium, bismuth, potassium, and rubidium.

This application is a division of application Ser. No. 663,266, filed10-22-1984 now abandoned.

BACKGROUND

This invention relates to a process for the production of allyl acetate.More particularly the present invention relates to the production ofallyl acetate by the acetoxylation of propylene.

It is known that allyl acetate can be produced by reacting propylene,oxygen, and acetic acid over a palladium-containing catalyst. Numerousexamples of promoters for the catalyst are reported in the literature.One of the more effective types of catalysts are those comprisingpalladium, potassium, and bismuth supported on an inert support. Evenwith such catalysts the optimum conditions have been found to give onlyabout 5-10% conversion of the propylene, with no more than about 90%selectivity to allyl acetate for a space time yield of about 250-320grams of allyl acetate per liter of catalyst per hour.

Obviously, it would be desirable to have a process which provided stillbetter selectivity, conversion, or space time yield.

An object of the present invention is to provide an improved process forthe acetoxylation of propylene.

Still another object of the present invention is to provide acomposition of matter suitable for use as a acetoxylation catalyst.

SUMMARY OF THE INVENTION

In accordance with the present invention a process is provided forpreparing allyl acetate comprising reacting propylene, acetic acid, andoxygen under suitable reaction conditions in the presence of a catalystconsisting essentially of palladium, potassium, bismuth, and a promotingamount of rubidium deposited on a support.

DETAILED DESCRIPTION

The catalysts of the present invention are prepared by depositing theactive components on the support and subsequently drying the resultingcomposite.

The supports include those typically used for acetoxylation catalysts.Examples include silica, aluminum oxide, aluminum silicates, silicates,titanium oxide, zirconium oxide, titanates, pumice silicium carbide,silica gel, spinels, and mixtures thereof. It is preferred to usesupports having a high chemical resistance to water and acetic acid suchas silica for example. Especially suitable are silica having a nitrogensurface area in the range of 40 to 350 m² /g.

The palladium of the catalyst can be in the form of free palladium metalor in the form of a compound of palladium which is preferably free ofhalogens, sulfur, and nitrogen. Examples of such compounds includepalladium acetate, palladium propionate, palladium acetylacetonate orpalladium hydroxide. It is currently preferred to employ a palladiumcarboxylate, especially palladium acetate.

The other active components are applied in the form of acetates orcompounds which will be converted to acetate either during the catalystprep or during the acetoxylation process. Examples include the formates,propionates, hydroxides, carbonates, phosphates, borates, citrates,tartrates, or lactates of the other active metal components.

The catalyst can be prepared in many different ways, for example acompound of the metal can be dissolved in a solvent, the supportimpregnated with the resulting solution and then dried. It is alsopossible, however, to impregnate the support successively with thecomponents which can then be converted, if required, by an intermediatetreatment, such as calcination, or chemical reactions such as forexample treatment with solutions of an alkali metal hydroxide, alkalimetal carbonate or a reducing agent. The catalysts can be prepared froma compound containing sulfur, nitrogen or halogen, which compound isthen converted on the support into an insoluble compound which issubstantially free of sulfur, nitrogen or halogen.

The currently preferred technique of preparing the catalyst, however,involves dissolving the metal components in glacial acetic acid, thenimpregnating the support, and then drying the resulting solid.

The amount of palladium employed on the catalyst can vary from about 1to about 3 weight percent, most preferably about 1 to about 2 weightpercent based on the weight of the support.

The amount of potassium can vary from about 3 to about 7 weight percent,more preferably about 4 to about 5 weight percent based on the weight ofthe support.

The amount of bismuth can vary from about 1 to about 3 weight percent,more preferably about 1.5 to 2.5 weight percent based on the weight ofthe support.

The rubidium should be present in an amount sufficient to result in animproved selectivity or space time yield over a catalyst containing onlyPd, Bi, and K. The specific amount needed will vary somewhat dependingupon the amounts of Pd, Bi and K in the catalyst. Typically, the amountof rubidium will be in the range of about 0.5 to about 1.5 weightpercent, most preferably about 1.2 weight percent based on the weight ofthe support.

In carrying out the acetoxylation propylene, oxygen, and acetic acid inthe gaseous phase are contacted with the inventive catalyst at atemperature in the range of about 100° C. to about 250° C. and pressuresof 1 to 25 absolute atmospheres. It is advantageous to use aconcentration ratio which ensures that the reaction mixture does notattain the known explosion limits. The simplest way to do this is tokeep the concentration of oxygen low, e.g. about 3 to 8% of the totalfeed employed. Generally, the non-reacted products may be recycled in acyclic process.

It has been typically noted that the preferred results are obtained ifthe reaction is carried out at a temperature in the range of about 160°C. to about 180° C. and a pressure of about 42 to 120 psig, morepreferably 75 to 100 psig.

The reaction mixture may also contain diluent gas which does notadversely affect the reaction such as nitrogen, carbon dioxide, andsaturated hydrocarbons.

It is also within the scope of the invention to include water along withthe reactants supplied to the catalyst. The amount of water employed isgenerally in the range of about 10 to about 30 weight percent of theacetic acid, more preferably about 15 to 25 weight percent.

The rate of contact of reactants and catalyst can vary over a wide rangedepending upon the conditions employed. Typically, however, the aceticacid would be supplied at a rate of about 0.4 to about 1.2 volumes pervolume of catalyst per hour, more preferably about 0.7 to 0.9. Thepropylene would typically be supplied at a rate sufficient to provideabout 0.5 to about 2 grams of propylene per milliliter of catalyst perhour, more preferably about 0.7 to about 1.5 g/ml/hr.

A further understanding of the present invention and the advantages thatit provides will be provided by the following examples.

In the following examples the general procedure involved in preparingthe catalysts involved dissolving the metal salts in glacial aceticacid, immersing the support with the solution, soaking the support for 2hours. Then the liquid was removed using a rotary evaporator and thecatalyst dried by heating for 3 hours in a convection oven at 120° C.The support employed was a silica sold by Davison Chemical Co. as highsurface area silica number G-59 of 8-12 mesh. The acetoxylations werecarried out in a metal pipe 1/2" by 20" packed with 50 ml of catalyst.Heat was supplied via a steam jacked around the pipe. After oxidationwas established it was continued for about 3 hours and then a totalsample of the reactor effluent was taken for 2 hours. The products wereanalyzed on a 5880 Hewlett Packard gas chromatograph using a 1/8"×36"Poropak Q column. The quantities of oxidation products were used tocalculate conversion, selectivity and catalyst productivity using thefollowing formulas:

EXAMPLE I

A series of catalysts were prepared using the acetates of Pd, Bi, K, andoptionally Rb. The results of the employment of those catalysts in theacetoxylation of propylene is summarized in Table I.

Unless noted otherwise the following conditions were employed:

Propylene--35 g/hr

Oxygen--4.5 L./hr

Acetic Acid feed (Neat or Aqueous*)--42 ml/hr

Pressure--75 psig

Temperature--170° C.

                                      TABLE I                                     __________________________________________________________________________    EFFECT OF CATALYST COMPONENTS ON REACTION RESULTS                                  HOAc Pd,.sup.(2)                                                                      K,.sup.(2)                                                                       Bi,.sup.(2)                                                                      Rb,.sup.(2)                                                                       Selectivity,                                                                        Conversion                                                                           STY,                                      Run No.                                                                            feed %  %  %  %   %     %      g/l/hr                                    __________________________________________________________________________    1    Neat 1.5                                                                              5.6                                                                              2.0                                                                              --  87.4  12.3   184                                       2    Aqueous                                                                            1.5                                                                              4.8                                                                              2.0                                                                              --  74.2  18.2   225                                       3    Neat 1.5                                                                              4.8                                                                              2.0                                                                              --  88.7  12.0   176                                       4.sup.(a)                                                                          Neat 1.5                                                                              4.8                                                                              2.0                                                                              --  88.8  18.8   277                                       5.sup.(b)                                                                          Neat 1.5                                                                              4.8                                                                              2.0                                                                              --  90.9  10.0   323                                       6    Neat 1.5                                                                              4.8                                                                              2.0                                                                              1.2 91.2  23.2   357                                       7.sup.(c)                                                                          Neat 1.5                                                                              4.8                                                                              2.0                                                                              1.2 92.7  12.3   398                                       8    Neat 1.5                                                                              4.8                                                                              2.0                                                                              0.6 74.4  23.9   295                                       __________________________________________________________________________     FOOTNOTES:                                                                    .sup.(a) Reaction at 180° C.                                           .sup.(b) Reaction at 180° C., propylene 75 g/hr                        .sup.(c) Propylene 75 g/hr.                                                   .sup.(2) Weight percent of metal based on weight of the support          

Runs 1 and 3 show that a catalyst consisting essentially of Pd, K, andBi gives a conversion of around 12 percent and less than 90%selectivity. Run 2 shows that the employment of water in the feed canincrease conversion but the selectivity is worse. Run 4 shows that aslight improvement in conversion can be obtained without too much effecton the selectivity by increasing the temperature. Run 5 shows thatincreasing the rate of propylene addition decreases conversion andincreases selectivity.

Run 6 demonstrates an embodiment of the present invention. A comparisonwith Run 3 shows that the inventive catalyst gives almost twice as muchconversion and better selectivity than a catalyst consisting essentiallyof Pd, K, and Bi. Since Run 7 was at a lower temperature than Run 5, Run7 also demonstrates that the conversion is much better with theinventive catalyst. Run 8 shows that even as little as 0.6 weightpercent Rb provides a significant improvement in conversion.

What is claimed is:
 1. A catalyst suitable for the acetoxylation ofpropylene consisting essentially of metals on a support said metalsconsisting essentially of potassium, bismuth, palladium, and a promotingamount of rubidium.
 2. A catalyst according to claim 1 wherein thecatalyst contains 1 to 3 weight percent palladium, 3 to 7 weight percentpotassium, and 1 to 3 weight percent bismuth, said weight percentagesbeing based on the support.
 3. A catalyst according to claim 2 whereinthe rubidium is in the range of about 0.5 to about 1.5 weight percentbased on the weight of the support.
 4. A catalyst according to claim 3wherein said support is silica.
 5. A catalyst according to claim 4wherein said catalyst contains about 1.5 weight percent palladium, about5 weight percent potassium, about 2.0 weight percent bismuth, and about1.2 weight percent rubidium based on the weight of the support.
 6. Acatalyst according to claim 5 wherein said catalyst is prepared byimpregnating said silica support with acetates of the metals and thendrying the catalyst.